5. Remove sheet from oven. Spoon rosemary-fat mixture over potatoes and turn again. Continue to roast until potatoes are well browned and rosemary is fragrant, 3 to 5 minutes. Season with salt and pepper to taste. Serve immediately.

Saving Fat for Cooking

Saving the leftover fat from duck is easy to do. Pour the warm fat through a fine-mesh strainer into a Mason jar and discard any solids.

Alternatively, let the fat cool and harden and then scoop it into the jar, leaving any solids behind.

Put the lid on the jar, label it, and refrigerate it for up to one month or freeze it for up to six months, adding more fat as desired.